Variable Coquina, Butterfly Shell, Wedge Shell
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Donacidae, Genus: Donax, Species: D. variabilis · Donacidae (Donax or Wedge Shell family) · Bivalve (Clam); Single valve (half-shell) typically found as a wedge or triangular shape.
Species
Donax variabilis (Confidence: 95%)
Shell Type
Bivalve (Clam); Single valve (half-shell) typically found as a wedge or triangular shape.
Family
Donacidae (Donax or Wedge Shell family)
Size
Approximately 15-20mm in length. This is a mature specimen; the species typically ranges from 10mm to 25mm.
Color & Pattern
Solid peach-orange coloration with faint concentric growth lines. The interior (unseen) would likely be a polished version of the exterior. This specimen lacks the 'sunray' radial bands sometimes seen, exhibiting a beautiful solid pastel phase.
Rarity
Very Common. These are among the most frequently found shells on Southeast US beaches, often appearing in the thousands.
Habitat
Found in the intertidal zone of sandy beaches, specifically the high-energy wash zone where waves break. They live just beneath the surface of the sand.
Geographic Range
Western Atlantic, specifically from Virginia south to Florida and along the Gulf Coast to Texas and Mexico.
Description
A small, sturdy, wedge-shaped bivalve with a smooth, glossy surface. The shell is inequilateral (the beak/umbo is toward one end) and features fine concentric growth rings. Its shape is often compared to a small wedge or a butterfly wing when both valves are joined at the hinge.
Key Features
Triangular/wedge shape; posterior end is shorter and steeply angled; smooth outer surface with subtle growth lines; highly variable color polymorphism within the species.
Collector Value
Minimal monetary value ($0.10 - $0.50) due to their abundance, but highly prized by amateur collectors for 'rainbow' displays because of their immense variety of colors and patterns.
Condition Notes
Good; the shell shows slight dulling from beach wear but retains its vibrant pigment and lacks significant chipping or predator boreholes. Grade: Fine.
Interesting Facts
Coquinas are famous for their 'surfing' behavior. They use a muscular foot to rapidly burrow into the sand between wave cycles to avoid being swept out to sea or eaten by shorebirds. They were historically used to make 'Coquina Broth' by Floridian coastal dwellers.
Ecological Role
Critical food source for shorebirds (like Sanderlings), crabs, and surf fish (like Pompano). They act as filter feeders, cleaning the water near the shore.
Similar Species
Donax fossor (striations are slightly different and generally found further north) and Donax texasiana (found in the Western Gulf).
Beach Finding Tips
Look at the 'swash line' as the tide recedes. You can often see live ones quickly digging back into the sand. To find empty shells, sift through shell hash piles near the high-tide mark.